1. Field of the Invention
The present invention relates to a rotating nut ball screw unit, and more particularly, to a rotating nut ball screw unit having a lubricating device.
2. Description of the Prior Art
In a rotating nut ball screw unit, the nut and the bearing shell is formed in one piece. The bearing shell is engaged with a working table, and the mechanical power is transmitted to the nut from a motor with a belt conveyer so as to drive the nut to rotate against the stationary screw bolt thereby removing the working table in the axial direction. As the screw bolt does not move, it is free from the problematic rotational inertia that causes a slender ball screw unit able to work with a high speed easily using a relatively small motor. With this merit, it is specially preferable to the semiconductor industry, the wood working machine, and the conveyance work that are considered to be modern and very important industries nowadays.
U.S. Pat. No. 5,809,838 and No. 6,732,600 disclosed a rotating nut ball screw unit with lubricating arrangement, which has a lubricating device as shown in FIG. 1. Referring to FIG. 1, a via hole 941 is bored through a bearing shell 940 to communicate an externally lubricating device with the inner space of the bearing 94. A nut 92 is also provided with a via hole 921 facing to the via hole 941 so as to transport the lubricating oil from the outside lubricating device to the inner wall of the nut 94 thereby lubricating a screw bolt 91 and balls 93. Meanwhile, the Lubricating means arranged as such has the following demerits, namely:
1. Some modifications have to be done on the nut 92 and the bearing shell 940 which might reduce the rigidity of the entire structure.
2. The ideal lubrication effect is seldom attained as continuous supply of the lubricant to the outer thread 910 of the screw bolt 91 and the inner thread 920 of the nut 92 is apt to meet interruption until the lubricant is full in all the space inside the nut 92.
Another contrivance disclosed in U.S. Pat. No. 6,364,058 provides a lubricant box at an end surface of the nut to lubricate the nut with a lubricating means. However, this structure is inapplicable to the rotating nut ball screw unit since the lubricant box attached to the nut will rotate along with the nut and force the lubricant to stick on the inner surface of an oil supply pipe unless some remedy is taken to overcome the centrifugal force.